Electric pressure indicator



June 28, 1949. R. c. FULLER 2,474,662

ELECTRIC PRESSURE INDICATOR Filed June 21, 1946 fitter-227.9

Patented June 2% 1949 UNITED STATES. PATENT OFFICE ELECTRIC PRESSURE INDICATOR Reginald Cyril Fuller, Brighton, England Application June 21, 1946, Serial No. 678,261 In Great Britain December 19, 1945 3 Claims. 1

This invention relates to fluid pressure operated electrical switches adapted to respond to the influence of hydraulic or gaseous fluid pressure for automatically making and/or breaking a circuit for apparatus actuted electrically and having a certain operative relationship with the hydraulic or gaseous fluid pressure generating means or means consuming energy from the source of fluid pressure or converting such pressure into kinetic energy. Or, the switch in one form of the invention may be adapted as a means for controlling the operation of a fluid pressure indicating gauge, signallying device or automatic controlling device.

Fluid pressure operated switches have been proposed heretofore in which a diaphragm exposed to the direct influence of the fluid pressure is deformed, against the influence of a spring by the fluid pressure to actuate contacts. Also the use of a stack of carbons, or a carbon body, in the circuit of a pressure indicating apparatus including an electrically operated pressure gauge has been proposed heretofore in which the pressure generated is transmitted to the carbon stack or body to vary the resistance of the stack or body for producing changes in the indicator of the gauge.

However in such heretofore proposed appliances the diaphragm actuated switching means was not suitable for use where the pressure applied varied L over a wide range and. consequently if such appliances were used under such conditions the diaphragm would yield beyond its predetermined elastic limit so as to cause the appliance to fail, or the diaphragm to acquire a permanent deformation resulting in the appliance becoming unreliable in operation. Or, in other of the said appliances the diaphragm, which is undesirable, is perforated to receive a contact member and/or it is subjected directly to the action of the spring when the fluid pressure falls below the load of the spring, and consequently is liable to be permanently deformed by the spring.

The object of the present invention is to provide a fluid pressure operated electrical switch incorporating a diaphragm and of sturdy and simple form which is cheap and simple to manufacture and which obviates the aforesaid disadvantages.

According to this invention a fluid pressure operated electrical switch of the type embodying an imperforated diaphragm exposed wholly on one side, with the exception of its clamped periphery to the influence of the fluid pressure to deform it to actuate the switch and in which the switch contacts are isolated from the diaphragm and actuated in one direction by resilient means which yieldingly opposes said deformation of the diaphragm, is characterised in that the said resilient means is an adjustable spring and by the provision therewith of stop means separate from the diaphragm preventing transmission of any or any but a relatively very small portion of the load of said adjustable spring to the diaphragm when the fluid pressure falls below the effective load of the spring, and also by the provision of an overload preventing member forming a positive stop against excessive deformation of the diaphragm beyond that produced by a predetermined minimum of the range of fluid pressure to which the switch is to respond.

In a practical embodiment of the invention, the contact referred to above also form part of the means for protecting the diaphragm from receiving the full available pressure of the spring when the fluid pressure drops below a predetermined minimum, and they take the form which will positively make or break the desired circuit with a high degree of accuracy immediately the diaphragm has been deformed out of its idle or nonoperative normal state to an extent which will ensure the diaphragm reasserting its normal or idle state when the pressure drops below the predetermined minimum without any lag or sticking by the diaphragm such as would arise if the diaphragm were deformed to a point nearer its elastic limit than to its normal or idle state. Contacts for such purpose could take the form of a carbon stack interposed between the said overload preventing member and the spring, the operative connection between the diaphragm and spring being in the form of a stud slidable through the overload preventing member and some of the contacts and making light contact with the diaphragm and a contact member forming with the carbon stack a positive stop for the spring.

In one practical embodiment of the invention the switch comprises a housing with opposed annular surfaces between which is gripped a flexible diaphragm, one of said surfaces being recessed to accommodate the head of a stud abutting against the face of the diaphragm remote from the face exposed to the fluid pressure, said stud sliding through said recessed surface to afford a switch actuating part, said stud head and the surface receiving it acting as an overload stop to prevent overloading of the diaphragm as the fluid pressure rises above a predetermined minimum pressure required to cause the stud to actuate the switch contacts for making or breaking the desired circuit.

If as aforesaid the contacts are carbon bodies in a carbon stack they may be annular members through which a shank of the stud slides freely, the stud being adapted under the influence of the fluid pressure to overcome the spring applying compression to the carbon bodies, but at fluid pressures below a predetermined minimum being protected by the carbon bodies from receiving any, or any but a relatively very light portion, of the pressure of the spring, whereby there will be an accurate and prompt response of the switch diaphragm to increase of fluid pressure above said predetermined minimum.

In order that the invention may-be clearly understood and readily carried into effect, drawings are appended hereto illustrating an embodiment thereof, and wherein,

Figure 1 is a sectional elevation view of a resistance device suitable for incorporation with the lubricating oil circuit of an internal combustion engine,

Figure 2 is a plan view of Figure 1, and

Figure 3 is a diagram showing the connection of the device in the electrical circuit of an electrically operated pressure indicator.

Referring to the drawings, the variable electric resistance embodies a stack of annular carbon rings I enclosedin an insulatingtube 2, pressure against a contact plate 2 on top of the carbon rings I being applied by an'adjustable device comprising'a coiled compression spring 4 interposed between the top contact plate 3 and a plate 5 carried'by an adjusting screw 6', such screw conveniently comprising a terminalto which can be connected one end of a. lead 1 from the gauge or signalling deviceindicated diagrammatically at 8 in Figure 2.

The said insulating tube forms part of, or is accommodated within a housing, which is partidiaphragm isengaged on the side remote from the fluid pressure receiving side by the flanged head I Ia'of a stud I I having a shank I-Ib passing loosely through a bottom contact plate I2, which plate in conjunction with the flanged head I Ia affords a positive stop for the diaphragm to prevent overloading of the diaphragm by the fluid pressure. The shank IIb also passes through the stack of carbon rings I, this stud being of insulating material. It will be seen that displacement of the diaphragm I 0 due to the pressure of hydraulic fluid causes the shank III) of the insulated stud I I to engage with the top contact plate -3 and thus relieve thestack of carbon rings from the pressure due to the-action'of the said coiled compression spring '4. Relaxation of the spring pressure on the stack of carbon rings produces a change in resistance which-can be recorded by asimple typerof indicating meter, orby varying the lumi- -=nosity-'of a lamp I -3 (see Figure 3) so that the lamp is only illuminated fully when there is no working pressure upon the fluid, or whensuch pressure contact plate I2 and diaphragm Ill gripped between them by an annular or gland nut I4 threaded on to the flange 9a. In practice the electrical circuit is completed through the stack of carbon rings I, e. g. one end ring of the stack I being connected electrically to the coil spring via the top contact plate 3 and thereby being electrically-connected to the aforesaid pressure adjusting screw 6 and the indicator 8 and the other end carbon ring being connected to the bottom contact-plate I2 which can be fitted with a terminal I2afor connection to a battery, or may be directly connected via the union device 9 to earth. Thedevice is arranged so that the maximum pressure actually breaks the circuit through the carbons after increasing the resistance.

It'will-be seen from the foregoing that excessive fluidpressure cannot damage the diaphragm III, by reason of the insulated stud head -I Ia abutting against the bottom contact plate I2 thereby restricting any further movement of the insulated stud and diaphragm after they have performed the function of varying the resistance and finally breaking the circuit at apredetermined pressure. Also that thediaphragm cannot be ruptured or subjected to undesirable strains by the load of the spring when the fluid pressure against the dia therein exposed wholly on one side, with the exception of its clamped periphery to the influence of the flui'dpressure to deform it to actuate the switch,'=switch contacts isolated from the diaphragm, resilient means actuating the contacts in one'dire'ction and yieldingly opposing said deformation of the diaphragm, said resilient means compris'i-ngan adjustable spring, stop means separate from the diaphragm preventing transmission of any, or any buta relatively very small portioniof the load of said adjustable spring to the diaphragm when the fluid pressure falls below the effective load of the spring, and an overload preventing memberforming a positive stop against excessive deformation of the diaphragm beyond that produced by a' predetermined minimum of .the range of fluid pressure to which the switch is to respond.

2. A switch according to claim 1 wherein the said contacts are arranged as a stack at least one of which is a carbon member interposed between saidoverloadpreventing member and a contact member, said latter member being engaged by the spring, and the overload stop also acting as a contact member and being connected to a terminaL'the spring forming an electrical connection across a further terminal and the said contact it engages, a stud slidable through the contacts and having a flanged L-head resting against the diap'hragmeand a stem engaging the contact subjected to the spring pressure, the contacts preventing the spring from overloading the diaphragm, when the fluid pressure is below a predetermined switch operating pressure.

3. A switch according to claim 2 comprising a housing in which are provided opposed annular surfaces between which is gripped the imperiorated flexible diaphragm one face of which is adapted to be exposed to the influence of fluid pressure, one of said surfaces being one face of an annular metallic member comprising the overload preventing member and being recessed to accommodate the head of the said stud, such head abutting against the face of the diaphragm remote from the face exposed to fluid pressure, the stem of said stud sliding through said annular member, the said spring being a coiled compression spring interposed between the appropriate contact member and a terminal fitting in the housing provided with means for adjusting the normal load of the spring.

REGINALD CYRIL FULLER.

6 REFERENCES CITED The following references are of record in the file of this patent:

Number Number UNITED STATES PATENTS 

